The Slovak day-ahead electricity market closed the second quarter of 2026 with an average peak index of 64,76 €/MWh and an average off-peak index of 132,67 €/MWh. The index named peak was therefore half as expensive as the index named off-peak, and this did not happen once: the inversion occurred on all 91 days of the quarter (OKTE, a. s.; public API of the XMtrade®/ISOT system, endpoint dam/indices, downloaded on 23 August 2026).
This text is a data overview of quarterly indices, not a trading recommendation and not a calculation for a specific load profile. It does not state why the prices arranged themselves this way — daily indices contain neither the structure of supply nor generation by technology, so any cause would be written in from outside.
Key indicators of the day-ahead market by quarter
The table below lines up six consecutive periods, from the second quarter of 2025 to the first 26 days of the third quarter of 2026. All values are simple averages of the daily indices in euro per MWh, with each day carrying a weight of one, and the last column shows on how many days of the period the peak index sat below the off-peak index.
| Period | Base | Peak | Off-peak | Days inverted |
|---|---|---|---|---|
| Q2 2025 (April–June) | 80,13 € | 53,09 € | 107,18 € | 89 of 91 |
| Q3 2025 (July–September) | 90,29 € | 76,25 € | 104,33 € | 79 of 92 |
| Q4 2025 (October–December) | 108,76 € | 121,32 € | 96,20 € | 10 of 92 |
| Q1 2026 (January–March) | 122,57 € | 128,35 € | 116,82 € | 32 of 90 |
| Q2 2026 (April–June) | 98,72 € | 64,76 € | 132,67 € | 91 of 91 |
| Q3 2026 (1–26 July) | 116,96 € | 84,50 € | 149,41 € | 26 of 26 |
The source is the same series of day-ahead indices that the short-term market operator publishes after every closed auction day. Every record used carries the publication status „final“.
What the peak index is and from which hour it is counted
The peak index is not the average of the more expensive hours of the day. It is the average of a fixed time window that does not move with wherever the price happens to sit on a given day. Two things that industry conversation tends to treat as one — the time boundary and the price level — are independent of each other.
The window itself can be established by calculation. The day of 26 July 2026 held 96 quarter-hour prices in the endpoint of hourly results. The average of all 96 gives 91,21, which is the published base index. The average of the 48 periods from 08:00 to 20:00 local time gives 40,27, which is the published peak index; the average of the remaining 48 periods gives 142,15, which is the published off-peak index. None of the four other windows tested — from 09:00 to 20:00, from 08:00 to 19:00, from 07:00 to 19:00 or from 09:00 to 21:00 — matches the published values.
The second quarter of 2026: inversion on all 91 days
The share of inverted days has risen three years running: 188 of 366 days in 2024, that is 51,37 %, then 209 of 365 days in 2025, that is 57,26 %, and finally 149 of 207 days of 2026 up to 26 July, that is 71,98 %. The second quarter of 2026 is the first full quarter in the series where the inversion held on every day.
The year-on-year comparison of the levels themselves points the same way. Against the second quarter of 2025 the base index rose by 23,19 %, the peak index by 21,99 % and the off-peak index by 23,79 %. Against the first quarter of 2026 the peak index fell by 49,55 %, while the off-peak index in the same comparison rose.
The spread between the off-peak and the peak index
The gap between the two indices reached 67,91 €/MWh in the second quarter of 2026, the widest in the whole series observed. In the second quarter of 2025 it was 54,09 €/MWh, and across the first 26 days of the third quarter of 2026 it stands at 64,91 €/MWh.
In the winter quarters the gap carries the opposite sign: in the fourth quarter of 2025 the off-peak index was 25,11 €/MWh below the peak index, and in the first quarter of 2026 it was 11,54 €/MWh below it. The denominator behind each of these figures is one period and the simple average of the daily indices within it, not the traded volume.
What these data do not say
The series of daily indices contains no generation by technology, no traded volumes split into peak and off-peak, and no prices of neighbouring markets: the fields for the Czech Republic, Hungary and Romania are empty in the responses for 2026. Any statement about a cause would therefore come from a source other than these figures.
Equally, the indices imply nothing about the price paid by a specific metering point. The day-ahead market is one component of electricity procurement and the tariff part of the bill does not sit in it. Nor does this series hold intraday auctions or bilateral contracts, so the day-ahead average is not the average of the market as a whole.
Conclusions
The peak index stood at 64,76 €/MWh in the second quarter of 2026, the off-peak index at 132,67 €/MWh. The ratio between them is 2,05-fold in favour of off-peak and the inversion held on all 91 days, the first such complete quarter in the series observed from the start of 2024. The base index of the period was 98,72 €/MWh, between the two outer values.
The name of the index marks a window, not a price level. An own calculation from the 96 quarter-hour prices of 26 July 2026 yields peak as the average of the periods from 08:00 to 20:00 and off-peak as the average of the remaining twelve hours. The match with the published values of 40,27 and 142,15 is exact to two decimal places.
What to watch next: whether the sign of the spread turns again in the fourth quarter of 2026 the way it turned in the fourth quarter of 2025, when the off-peak index was 25,11 €/MWh below the peak index. Daily values accumulate after every closed auction day in the index endpoint, whose parameters are described by the documentation of the public interface.
Analysis, not personalised advice. Before a transaction decision, verify the tariff value or the wording of the regulation directly with the network operator or the regulator.